sincerity / purity of devotion
Form IV maṣdar (إِفْعَال). Verb: أَخْلَصَ (to be sincere/purify). مُخْلِصٌ (sincere person). Surah al-Ikhlāṣ (112) is named 'Sincerity/Purity.'
Ikhlāṣ means purifying one's intention for God alone - no deed is accepted without it. Surah al-Ikhlāṣ distills pure monotheism into four verses.